Fuel cells are being developed for use in automotive propulsion systems as alternatives for the internal combustion engine in buses, vans, and passenger cars. The major motivations for developing fuel cell powered vehicles are low emissions of pollutants, high fuel energy conversion efficiencies, superior acceleration, low noise and vibration, and the possibility of using coal or biomassderived alcohols rather than petroleum-based fuels, although petroleum-based fuels can also be used.
The two most important operational requirements for a stand-alone fuel cell power system for a vehicle are the ability to start up quickly and the ability to supply the necessary power on demand for the dynamically fluctuating load. The rapid start-up requirement is obvious. An example of the dynamic performance requirement is given in FIG. 1, which shows the simulated velocity and power profiles for a small car, the IETV-1, operated on the Simplified Federal Urban Driving Schedule (SFUDS). On this schedule the power varies 15 times over 6 min; in actual driving the power fluctuations are typically more numerous and more complex.
Alcohols such as methanol and ethanol are likely fuels for use in fuel cells for transportation applications. Methanol is a commodity chemical that is manufactured from coal, natural gas, and other feedstocks, while ethanol is often produced from grain. For use in a fuel cell, however, alcohol must first be converted (reformed) to a hydrogen-rich gas mixture. The desired features for such a fuel reformer include rapid start-up, good dynamic response, high fuel conversion, small size and weight, simple construction and operation, and low cost.
Methanol has been used in steam reforming for providing a hydrogen-rich gas stream for mobile combustion engines, see Konig et al, U.S. Pat. No. 4,716,859, and water as a reaction product from a fuel cell has been recycled for use in steam reforming of methanol, see Baker, U.S. Pat. No. 4,365,006. Steam reforming of methanol is endothermic and complicates, by its energy requirement, its use in a vehicle.
Supplying the hydrogen-rich gas on demand in an intermittent variable demand environment also is a difficult requirement to meet and has been addressed by Ohsaki, et al, U.S. Pat. No. 4,988,580, but this suggestion is not applicable to a small, mobile system. The catalytic, exothermic partial oxidation-reforming of fuels to produce hydrogen-rich gas streams is known, see Rao, U.S. Pat. No. 4,999,993, but the use of a partial oxidation-reformer has not been used in a vehicle to accomplish the purposes of this invention.